EP3783376A1

EP3783376A1 - Electric motor diagnosing device

Info

Publication number: EP3783376A1
Application number: EP18915192.1A
Authority: EP
Inventors: Toshihiko Miyauchi; Makoto Kanemaru
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2018-04-17
Filing date: 2018-04-17
Publication date: 2021-02-24
Anticipated expiration: 2038-04-17
Also published as: WO2019202651A1; JPWO2019202651A1; KR102376883B1; JP6945728B2; EP3783376A4; CN111936874B; EP3783376B1; KR20200130405A; CN111936874A

Abstract

The electric motor diagnosing device includes a current detection circuit (7) for detecting current of an electric motor (5), and a calculation processing unit (10) which receives output of the current detection circuit (7) and performs determination for winding short-circuit abnormality of the electric motor (5), wherein the calculation processing unit (10) includes a driving state determination unit (41) for determining the driving state of the electric motor (5), and an initial negative-phase-sequence current analysis unit (31) for analyzing initial negative-phase-sequence current in a normal state, and performs determination for winding short-circuit of the electric motor using, as an evaluation value, a difference between negative-phase-sequence current calculated from current of the electric motor during driving and the initial negative-phase-sequence current. Thus, negative-phase-sequence admittance is not calculated and therefore short-circuit failure in stator windings of the electric motor can be detected accurately.

Description

TECHNICAL FIELD

The present disclosure relates to an electric motor diagnosing device.

BACKGROUND ART

There are a lot of electric motors in a plant, and diagnosis for the equipment thereof is conducted by person's senses in a maintenance department. In particular, for electric motors which are of high importance, regular diagnosis is needed and thus the cost increases. Further, in an electric motor, a gap or damaged part of an insulation material caused by mechanical stress and thermal deterioration induces layer short-circuit through discharge or the like and this can suddenly lead to insulation breakage. Therefore, once deterioration in an electric motor begins, the deterioration is only going to progress further.
Accordingly, there is increasing interest in technology for constantly monitoring electric motors. However, many of electric motor constantly monitoring technologies are based on the premise that various measurement devices such as sensors are attached for each electric motor. The measurement devices are, for example, a torque meter, an encoder, an acceleration sensor, and the like. However, application to a motor control center which performs centralized management for hundreds to thousands of motors is not realistic because the number of wires increases. Therefore, there is a need for a device that is capable of simply diagnosing the states of electric motors on the basis of information about current and voltage measured in a motor control center without using special sensors, and achieves improved reliability, productivity, and safety.
In this regard, the applicant has proposed an electric motor diagnosing device including an electric motor, a diagnosing device, a current sensor, and a voltage sensor (see Patent Document 1). The electric motor diagnosing device is provided with a current detection circuit for detecting current and a voltage detection circuit for detecting voltage of the electric motor on the basis of voltage of a main circuit of a power supply, and performs determination and detection for winding short-circuit while distinguishing power supply imbalance even when load torque varies during operation of the electric motor, on the basis of negative-phase-sequence current, negative-phase-sequence voltage, positive-phase-sequence current, and negative-phase-sequence admittance.

CITATION LIST

PATENT DOCUMENT

Patent Document 1: Japanese Patent No. 6099852

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

In short-circuit diagnosis for stator windings in the electric motor diagnosing device disclosed in Patent Document 1, determination for winding short-circuit is performed on the basis of an evaluation value A using the negative-phase-sequence admittance (A = |Isn - Yn·Vsn| in Expression (10) of Patent Document 1, where Isn is negative-phase-sequence current, Yn is negative-phase-sequence admittance, and Vsn is negative-phase-sequence voltage). Here, in calculating initial negative-phase-sequence admittance Yn, if the power supply imbalance is small, the negative-phase-sequence current value is small, so that error of the negative-phase-sequence admittance Yn increases. Increase in error of the initial negative-phase-sequence admittance Yn increases error of the value of the second term on the right-hand side of the winding short-circuit evaluation value, and this might lead to erroneous detection of winding short-circuit. Therefore, a method not using the negative-phase-sequence admittance Yn is required.
The present disclosure has been made to solve the above problem, and an object of the present disclosure is to provide an electric motor diagnosing device capable of accurately detecting short-circuit failure in stator windings of an electric motor without calculating negative-phase-sequence admittance.

SOLUTION TO THE PROBLEMS

An electric motor diagnosing device according to the present disclosure is an electric motor diagnosing device including: a current detection circuit for detecting current of an electric motor; and a calculation processing unit which receives output of the current detection circuit and performs determination for winding short-circuit abnormality in the electric motor, wherein the calculation processing unit includes a driving state determination unit which calculates an effective value from current of the electric motor to determine a driving state thereof, an initial negative-phase-sequence current analysis unit for analyzing initial negative-phase-sequence current in a normal state, and a winding short-circuit determination unit which calculates an evaluation value for winding short-circuit on the basis of a difference between negative-phase-sequence current calculated from current of the electric motor during driving and the analyzed initial negative-phase-sequence current, and performs determination for winding short-circuit of the electric motor through comparison between the evaluation value and a set threshold.

EFFECT OF THE INVENTION

The electric motor diagnosing device according to the present disclosure performs determination for winding short-circuit, using, as the evaluation value, the difference between the negative-phase-sequence current calculated from current of the electric motor during driving and the initial negative-phase-sequence current. Thus, negative-phase-sequence admittance is not calculated and therefore short-circuit failure in stator windings of the electric motor can be detected accurately.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] FIG. 1 is a circuit configuration diagram showing an electric motor diagnosing device according to embodiment 1.
[FIG. 2] FIG. 2 conceptually illustrates winding short-circuit.
[FIG. 3] FIG. 3 is a configuration diagram of a calculation processing unit in the electric motor diagnosing device according to embodiment 1.
[FIG. 4] FIG. 4 is a flowchart for analyzing initial negative-phase-sequence current using the electric motor diagnosing device according to embodiment 1.
[FIG. 5] FIG. 5 is a flowchart for performing winding short-circuit determination using the electric motor diagnosing device according to embodiment 1.
[FIG. 6] FIG. 6 is a circuit configuration diagram showing an electric motor diagnosing device according to embodiment 2.
[FIG. 7] FIG. 7 is a configuration diagram of a calculation processing unit in the electric motor diagnosing device according to embodiment 2.
[FIG. 8] FIG. 8 is a flowchart for analyzing initial negative-phase-seguence current using the electric motor diagnosing device according to embodiment 2.
[FIG. 9] FIG. 9 is a flowchart for performing winding short-circuit determination using the electric motor diagnosing device according to embodiment 2.
[FIG. 10] FIG. 10 shows the correspondence relationship between a voltage imbalance rate and negative-phase-sequence current, used in an electric motor diagnosing device according to embodiment 3.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described with reference to the drawings. In the drawings, the same reference characters denote the same or corresponding parts.

Embodiment 1

Hereinafter, an electric motor diagnosing device according to embodiment 1 will be described with reference to FIG. 1 to FIG. 5.
FIG. 1 is a circuit configuration diagram showing the electric motor diagnosing device according to embodiment 1, which is mainly used in a control center which is an enclosed switchboard. In the drawing, a main circuit 1 of a power supply led from a power system is provided with a circuit breaker 2, an electromagnetic contactor 3, and an instrument transformer 4 for detecting load current of the main circuit 1. Further, an electric motor 5 which is a load is connected, and mechanical equipment 6 is driven by the electric motor 5.
An electric motor diagnosing device 100 includes a current detection circuit 7 connected to the instrument transformer 4, a calculation processing unit 10, a storage device 11, a setting circuit 12, an indication unit 13, a drive circuit 14, an external output unit 15, and a communication circuit 16.
The current detection circuit 7 converts load current of the main circuit 1 detected by the instrument transformer 4, to a predetermined signal such as phase current of the electric motor 5, to detect current of the electric motor, and outputs the signal to the calculation processing unit 10 and the storage device 11. That is, the current detection circuit 7 detects current of the electric motor 5 from current flowing through the main circuit 1 of the power supply connected to the electric motor 5.
The calculation processing unit 10 receives output of the current detection circuit 7, and calculates negative-phase-sequence current and the like through analysis on current of the electric motor, to perform determination for winding short-circuit during operation of the electric motor.
The calculation processing unit 10 includes a central processing unit (CPU) as a calculation processing device. As a calculation processing device, various logic circuits such as an application specific integrated circuit (ASIC), an integrated circuit (IC), and a digital signal processor (DSP), various signal processing circuits, and the like may be provided.
The storage device 11 is connected to the calculation processing unit 10 and the setting circuit 12, and transmits/receives data to/from the calculation processing unit 10. The storage device 11 includes a random access memory (RAM) from/into which data can be read/written by the calculation processing unit 10, a read only memory (ROM) or a nonvolatile memory (EEPROM: electrically erasable programmable read only memory) from which data can be read by the calculation processing unit 10, and the like.
The setting circuit 12 connected to the storage device 11 has a set key, and by pressing (e.g., holding down) the set key, data in an initial normal state is stored and retained in the storage device 11. The data can be stored until the set key is canceled.
The indication unit 13 is connected to the calculation processing unit 10, and indicates a detected physical quantity such as load current, and an abnormal state, a warning, and the like when the calculation processing unit 10 has detected abnormality in the electric motor 5.
The drive circuit 14 is connected to the calculation processing unit 10, and outputs a control signal for opening/closing the electromagnetic contactor 3 on the basis of a result of calculation performed by the calculation processing unit 10 on the basis of a current signal detected by the instrument transformer 4.
The external output unit 15 outputs a signal of an abnormal state, a warning, and the like from the calculation processing unit 10, to outside.
An external monitoring device 200 is formed from a personal computer (PC) or the like, and is connected to one or a plurality of electric motor diagnosing devices 100. The external monitoring device 200 receives information of the calculation processing unit 10 via the communication circuit 16 as necessary, and monitors the operation condition of the electric motor diagnosing device 100. Connection between the external monitoring device 200 and the communication circuit 16 of the electric motor diagnosing device 100 may be made using a cable or wirelessly. The connection may be made via the Internet by constructing a network among the plurality of electric motor diagnosing devices 100.
FIG. 2 conceptually illustrates winding short-circuit subjected to diagnosis in the present disclosure. In the drawing, it is assumed that short-circuit occurs in phase a and short-circuit current If flows, and the number of short-circuited winding turns is denoted by Nf. A short-circuit rate µ, which is a ratio of Nf to the number of whole winding turns N, is generalized as shown below: $μ = Nf / N .$
In addition, in the stator windings of the electric motor 5, either of short-circuit in the same layer and short-circuit between layers can occur. In the present embodiment, these two types of short-circuit are both diagnosed as winding short-circuit.
In the present disclosure, rating information for the electric motor 5 need not be inputted before start of operation.
FIG. 3 is a configuration diagram schematically showing the calculation processing unit 10 in the electric motor diagnosing device according to embodiment 1. The calculation processing unit 10 includes a current conversion unit 20, an initial analysis unit 30, a determination unit 40, an analysis unit 50, and an abnormality determination unit 60.
The current conversion unit 20 includes an effective value calculation unit 21 and a negative-phase-sequence current calculation unit 22, and calculates negative-phase-sequence current Isn by the following Expression (1) through symmetric coordinate conversion processing on the basis of three-phase currents detected by the current detection circuit 7.
[Mathematical 1] $\begin{array}{l} I_{sn} = \frac{1}{3} (I_{u} + a^{2} I_{v} + {aI}_{w}) \\ a = e^{j \frac{2}{3} π} \end{array}$
Here, Isn is the negative-phase-sequence current, Iu is u-phase current, Iv is v-phase current, and Iw is w-phase current.
The initial analysis unit 30 includes an initial negative-phase-sequence current analysis unit 31. The initial negative-phase-sequence current analysis unit 31 analyzes a negative-phase-sequence current value Isn in a normal state before winding short-circuit determination. For example, negative-phase-sequence current values for one month are calculated, and an averaged value thereof is used as an initial negative-phase-sequence current value IsnO.
The determination unit 40 includes a driving state determination unit 41. The driving state determination unit 41 determines the driving state of the motor on the basis of the effective value of current calculated by the effective value calculation unit 21. Determination for the driving state of the motor may be performed on the basis of, instead of the effective value of current, the instantaneous value of current or an ON/OFF signal of the electromagnetic contactor 3.
The analysis unit 50 includes an evaluation value analysis unit 51, and performs analysis for determination to be performed in a winding short-circuit determination unit 61 of the abnormality determination unit 60. The evaluation value analysis unit 51 calculates an evaluation value A = |Isn - Isn0|.
Next, calculation for the evaluation value A will be described. Winding short-circuit is short-circuit between coil wires. When winding short-circuit occurs, the three-phase stator currents become asymmetric, and therefore detection can be performed from a negative-phase-sequence component. Where the short-circuit rate when winding short-circuit occurs in a part of stator windings of a three-phase induction electric motor is denoted by µ (µ = Nf/N) and µ << 1 is assumed, the following relational expressions are obtained among positive-phase-sequence voltage Vsp, negative-phase-sequence voltage Vsn, positive-phase-sequence current Isp, and negative-phase-sequence current Isn.
[Mathematical 2] $[\begin{matrix} {\tilde{I}}_{sp} \\ {\tilde{I}}_{sn} \end{matrix}] = [\begin{matrix} Y_{pp} & Y_{pn} \\ Y_{np} & Y_{nn} \end{matrix}] [\begin{matrix} {\tilde{V}}_{sp} \\ {\tilde{V}}_{sn} \end{matrix}]$
[Mathematical 3] $Y_{pn} = Y_{np} = \frac{μ^{2}}{3 ({jμωL}_{ls} + r_{f} + {μr}_{s})}$
[Mathematical 4] $\begin{array}{l} Y_{pp} = Y_{p} + Y_{pn} \\ = \frac{r_{r} + {jsωL}_{r}}{{sω}^{2} L_{m}^{} + (r_{s} + {jωL}_{s}) (r_{r} + {jsωL}_{r})} + \frac{μ^{2}}{3 ({jμωL}_{ls} + r_{f} + {μr}_{s})} \end{array}$
[Mathematical 5] $\begin{array}{l} Y_{nn} = Y_{n} + Y_{np} \\ = \frac{r_{r} + j (2 - s) {ωL}_{r}}{(2 - s) ω^{2} L_{m}^{} + (r_{s} + {jωL}_{s}) (r_{r} + j (2 - s) {ωL}_{r})} + \frac{μ^{2}}{3 ({jμωL}_{ls} + r_{f} + {μr}_{s})} \end{array}$
Here, Ypp is admittance of a positive phase sequence-positive phase sequence component, Ynn is admittance of a negative phase sequence-negative phase sequence component, Ypn is admittance of a positive phase sequence-negative phase sequence component, Ynp is admittance of a negative phase sequence-positive phase sequence component, Yn is negative-phase-sequence admittance, ω is a power supply angular velocity, rs is stator resistance, rr is rotor resistance, rf is short-circuit resistance, Ls is stator leakage inductance, Lr is rotor leakage inductance, Lm is excitation inductance, and µ is the short-circuit rate.
A non-diagonal component Ypn of the admittance Y can be used as an index for winding short-circuit, but it is not easy to calculate the non-diagonal component Ypn in an actual device. Therefore, here, a method of measuring and monitoring only negative-phase-sequence current Isn by analyzing normal-state data of initial negative-phase-sequence current IsnO, is adopted.
When winding short-circuit does not occur (µ = 0), the non-diagonal component Ypn of the admittance Y is zero, and therefore the following is satisfied. $Isn = Yn \cdot Vsn = Isn 0$
When winding short-circuit occurs, Isn changes as follows. $Isn = Yn \cdot Vsn + Ypn \cdot Vsp = Isn 0 + Ypn \cdot Vsp$
That is, with the initial negative-phase-sequence current IsnO analyzed, only Isn and IsnO are measured, and the following evaluation value A is used as an index. $Evaluation value A = |Isn - Isn 0|$
Thus, occurrence of winding short-circuit can be detected.
At the initial period when an electric motor is installed, initialization is performed (negative-phase-sequence admittance Yn is calculated) assuming that winding short-circuit has not occurred yet, and thereafter, the evaluation value A in Expression (8) is monitored to perform determination for winding short-circuit.
The abnormality determination unit 60 includes a winding short-circuit determination unit, and determines whether or not winding short-circuit has occurred on the basis of whether or not the evaluation value A calculated by the evaluation value analysis unit 51 exceeds a predetermined threshold δ1. The threshold δ1 is a value that differs depending on the rating of the electric motor 5.
Next, a process for diagnosis using the electric motor diagnosing device 100 will be described with reference to FIG. 4 and FIG. 5.
FIG. 4 is a flowchart for analyzing initial negative-phase-sequence current using the electric motor diagnosing device according to embodiment 1. Current (current for each phase) of the electric motor 5 is acquired by the current detection circuit 7 (step S11), and the effective value calculation unit 21 calculates the effective value of the current (step S12). The driving state determination unit 41 determines whether or not the electric motor 5 is in a driven state, on the basis of the effective value of the current, and if it is determined that the electric motor 5 is in a driven state (Yes in step S13), the negative-phase-sequence current calculation unit 22 calculates negative-phase-sequence current (step S14). Whether or not the number of times the negative-phase-sequence current is calculated exceeds a predetermined number of times, is determined. If it is determined that the predetermined number of times is exceeded (Yes in step S15), the negative-phase-sequence current values for the predetermined number of times are averaged, and the averaged value is used as the initial negative-phase-sequence current value IsnO (step S16). The initial negative-phase-sequence current value IsnO is stored in the storage device 11. If the number of times the negative-phase-sequence current is calculated is smaller than the predetermined number of times (No in step S15), current of the electric motor is acquired again to repeat processing from step S11 to step S15 until reaching the predetermined number of times.
After the initial negative-phase-sequence current value IsnO is calculated, diagnosis for winding short-circuit determination is performed.
FIG. 5 is a flowchart for performing winding short-circuit determination. Current (current for each phase) of the electric motor 5 is acquired by the current detection circuit 7 (step S21), and the effective value calculation unit 21 calculates the effective value of the current (step S22). The driving state determination unit 41 determines whether or not the electric motor 5 is in a driven state, on the basis of the effective value of the current, and if it is determined that the electric motor 5 is in a driven state (Yes in step S23), the negative-phase-sequence current calculation unit 22 calculates negative-phase-sequence current Isn (step S24).
Next, the evaluation value analysis unit 51 calculates the evaluation value A in Expression (8) from the initial negative-phase-sequence current IsnO calculated in step S16 in FIG. 4 and stored in the storage device 11 and the negative-phase-sequence current Isn calculated in step S24 (step S25). The winding short-circuit determination unit 61 compares the evaluation value A and the predetermined threshold δ1. If A ≥ δ1 is satisfied (Yes in step S26), the winding short-circuit determination unit 61 determines that winding short-circuit has occurred, and outputs the result to outside (step S27).
In the case of A < δ1 in step S26, the process returns to step S21 to acquire current (current for each phase) of the electric motor 5 again.
As described above, in embodiment 1, a difference from the initial value of the negative-phase-sequence current is used as the evaluation value A for winding short-circuit, and determination for winding short-circuit is performed through comparison between the evaluation value A and the predetermined threshold δ1. Therefore, the initial state can be offset and negative-phase-sequence admittance is not calculated. Thus, it is possible to accurately detect short-circuit failure in the stator windings of the electric motor. In addition, since a voltage detection circuit is not needed, it becomes possible to provide an electric motor diagnosing device capable of accurately detecting short-circuit failure in stator windings of an electric motor while suppressing power consumption, with a simple configuration.
In the present embodiment, it is assumed that the voltage imbalance rate is small. This is because, if the voltage imbalance rate is great, the negative-phase-sequence current value changes depending on variation in load torque, and thus there is a high possibility that erroneous detection occurs in winding short-circuit determination. In a system used in the control center which is an enclosed switchboard, exemplified in the present embodiment, the magnitude of the voltage imbalance rate can be selected in advance on the basis of load balance. In the present embodiment, a system having a small voltage imbalance rate as selected can be adopted. Alternatively, as described later, measurement for the voltage imbalance rate may be performed in parallel, or the value thereof may be acquired in advance, and then whether or not the present embodiment is applicable may be determined.

Embodiment 2

Hereinafter, an electric motor diagnosing device according to embodiment 2 will be described with reference to FIG. 6 to FIG. 9.
FIG. 6 is a circuit configuration diagram showing an electric motor diagnosing device according to embodiment 2, and the difference from embodiment 1 is that the main circuit 1 is provided with an instrument voltage transformer 8 for detecting voltage of the main circuit 1, and the electric motor diagnosing device 100 is provided with a voltage detection circuit 9 connected to the instrument voltage transformer 8. The other configurations are the same as those in embodiment 1.
The voltage detection circuit 9 detects line-to-line voltages of the main circuit 1 of the power supply connected to the electric motor, converts these to predetermined signals such as phase voltages of the electric motor 5, to detect voltage of the electric motor, and outputs the signal to the calculation processing unit 10 and the storage device 11.
The calculation processing unit 10 receives outputs of the current detection circuit 7 and the voltage detection circuit 9, and calculates negative-phase-sequence current, a voltage imbalance rate, and the like through analysis on voltage and current of the electric motor 5, to perform determination and detection for winding short-circuit during operation of the electric motor.
FIG. 7 is a configuration diagram schematically showing the calculation processing unit 10 in the electric motor diagnosing device according to embodiment 2. The calculation processing unit 10 includes a current voltage conversion unit 20a, the initial analysis unit 30, the determination unit 40, the analysis unit 50, and the abnormality determination unit 60.
The current voltage conversion unit 20a includes the effective value calculation unit 21, the negative-phase-sequence current calculation unit 22, and a voltage imbalance rate calculation unit 23, and calculates negative-phase-sequence current Isn by Expression (1) described in embodiment 1 through symmetric coordinate conversion processing on the basis of three-phase currents detected by the current detection circuit 7.
The voltage imbalance rate calculation unit 23 calculates a voltage imbalance rate Vunbal, using phase voltages for the respective phases or line-to-line voltages. In the case of calculating the voltage imbalance rate Vunbal from, for example, line-to-line voltages, the following expression is used. $Vunbal = ((greatest difference between line-to-line voltages and average voltage) / average voltage) \times 100 %$
That is, Vunbal is the greatest one of the following: $(Vuv - Vavg) / Vavg \times 100 %,$
$(Vvw - Vavg) / Vavg \times 100 %,$
and $(Vwu - Vavg) / Vavg \times 100 % .$
Here, average voltage Vavg = (Vuv + Vvw + Vwu)/3.
In addition, Vuv is line-to-line voltage between phase u and phase v, Vvw is line-to-line voltage between phase v and phase w, and Vwu is line-to-line voltage between phase w and phase u.
In the voltage imbalance rate calculation unit 23, it is preferable that the negative-phase-sequence current is calculated only when the voltage imbalance rate Vunbal is not greater than 1%, and the negative-phase-sequence current is not calculated when the voltage imbalance rate is greater than 1%. This is because, if the voltage imbalance rate is great, the negative-phase-sequence current value changes depending on variation in load torque, and therefore there is a high possibility that erroneous detection occurs in winding short-circuit determination. Also for short-circuit determination, limitation is set so that the determination is performed only when the voltage imbalance rate is not greater than, for example, 1%, whereby winding short-circuit determination accuracy can be enhanced.
The initial analysis unit 30 includes the initial negative-phase-sequence current analysis unit 31. The initial negative-phase-sequence current analysis unit 31 analyzes a negative-phase-sequence current value Isn in a normal state before winding short-circuit determination. As in embodiment 1, for example, negative-phase-sequence current values for one month are calculated, and an averaged value thereof is used as an initial negative-phase-sequence current value IsnO.
The determination unit 40 includes the driving state determination unit 41 and a voltage imbalance determination unit 42. The driving state determination unit 41 determines the driving state of the motor on the basis of the effective values of current and voltage calculated by the effective value calculation unit 21. Determination for the driving state of the motor may be performed on the basis of, instead of the effective values of current and voltage, the instantaneous value of current or voltage, or an ON/OFF signal of the electromagnetic contactor 3.
The voltage imbalance determination unit 42 determines whether or not the voltage imbalance rate Vunbal is greater than a predetermined threshold δ2. The threshold δ2 is set at, for example, 1% as described above.
The analysis unit 50 includes the evaluation value analysis unit 51, and performs analysis for determination to be performed in the winding short-circuit determination unit 61 of the abnormality determination unit 60. The evaluation value analysis unit 51 calculates the evaluation value A = |Isn - Isn0| in Expression (8). The calculation method for the evaluation value A is the same as in embodiment 1.
That is, with the initial negative-phase-sequence current IsnO analyzed, only Isn and IsnO are measured, and the evaluation value A is used as an index, whereby occurrence of winding short-circuit can be detected.
At this time, by being limited to the case where the voltage imbalance rate Vunbal is not greater than, for example, 1%, detection can be accurately performed. In addition, at the initial period when the electric motor 5 is installed, initialization is performed (negative-phase-sequence admittance Yn is calculated) assuming that winding short-circuit has not occurred yet, and thereafter, the evaluation value A in Expression (8) is monitored to perform determination for winding short-circuit.
The configuration of the abnormality determination unit 60 is the same as that in embodiment 1, i.e., includes the winding short-circuit determination unit and determines whether or not winding short-circuit has occurred on the basis of whether or not the evaluation value A calculated by the evaluation value analysis unit 51 exceeds the predetermined threshold δ1.
Next, a process for diagnosis using the electric motor diagnosing device 100 will be described with reference to FIG. 8 and FIG. 9.
FIG. 8 is a flowchart for analyzing initial negative-phase-sequence current using the electric motor diagnosing device according to embodiment 2. Current (current for each phase) of the electric motor 5 is acquired by the current detection circuit 7, and voltages (line-to-line voltages or phase voltages) of the electric motor 5 are acquired by the voltage detection circuit 9 (step S31). The effective value calculation unit 21 calculates the effective values of the current and the voltage (step S32). The driving state determination unit 41 determines whether or not the electric motor 5 is in a driven state, on the basis of the effective values of the current and the voltage. If it is determined that the electric motor 5 is in a driven state (Yes in step S33), the voltage imbalance rate calculation unit 23 calculates the voltage imbalance rate Vunbal (step S34) .
The voltage imbalance rate Vunbal is compared with the predetermined threshold δ2, and if voltage imbalance rate Vunbal ≤ δ2 is satisfied (Yes in step S35), the negative-phase-sequence current calculation unit 22 calculates the negative-phase-sequence current (step S36). Whether or not the number of times the negative-phase-sequence current is calculated exceeds a predetermined number of times is determined, and if it is determined that the predetermined number of times is exceeded (Yes in step S37), the negative-phase-sequence current values for the predetermined number of times are averaged, and the averaged value is used as the initial negative-phase-sequence current value IsnO (step S38). The initial negative-phase-sequence current value IsnO is stored in the storage device 11. If the number of times the negative-phase-sequence current is calculated is smaller than the predetermined number of times (No in step S37), current of the electric motor is acquired again to repeat processing from step S31 to step S37 until reaching the predetermined number of times.
After the initial negative-phase-sequence current value IsnO is calculated, diagnosis for winding short-circuit determination is performed.
FIG. 9 is a flowchart for performing winding short-circuit determination. Current (current for each phase) of the electric motor 5 is acquired by the current detection circuit 7, and voltages (line-to-line voltages or phase voltages) of the electric motor 5 are acquired by the voltage detection circuit 9 (step S41). The effective value calculation unit 21 calculates the effective values of the current and the voltage (step S42). The driving state determination unit 41 determines whether or not the electric motor 5 is in a driven state, on the basis of the effective values of the current value and the voltage value. If it is determined that the electric motor 5 is in a driven state (Yes in step S43), the voltage imbalance rate calculation unit 23 calculates the voltage imbalance rate Vunbal (step S44) .
The voltage imbalance rate Vunbal is compared with the predetermined threshold δ2, and if voltage imbalance rate Vunbal ≤ δ2 is satisfied (Yes in step S45), the negative-phase-sequence current calculation unit 22 calculates the negative-phase-sequence current Isn (step S46). Next, the evaluation value analysis unit 51 calculates the evaluation value A in Expression (8) from the initial negative-phase-sequence current IsnO calculated in step S38 in FIG. 8 and stored in the storage device 11 and the negative-phase-sequence current Isn calculated in step S46 (step S47). The winding short-circuit determination unit 61 compares the evaluation value A and the predetermined threshold δ1, and if A ≥ δ1 is satisfied (Yes in step S48), the winding short-circuit determination unit 61 determines that winding short-circuit has occurred, and outputs the result to outside (step S49) .
In the case of A < δ1 in step S48, the process returns to step S41 to acquire current (current for each phase) and voltages (line-to-line voltages or phase voltages) of the electric motor 5 again.
As described above, embodiment 2 provides the same effects as those in embodiment 1. Further, in the case where the voltage imbalance rate Vunbal is unknown or estimated to be great, the voltage imbalance rate Vunbal is calculated, and if the voltage imbalance rate Vunbal is greater than the predetermined threshold δ2, e.g., 1%, short-circuit determination based on the negative-phase-sequence current is not performed. Thus, error in short-circuit determination is suppressed. As a matter of course, if the calculated voltage imbalance rate Vunbal is smaller than the predetermined threshold δ2, winding short-circuit determination is performed in accordance with the flowcharts shown in FIG. 8 and FIG. 9.

Embodiment 3

In embodiments 1 and 2, the initial negative-phase-sequence current value IsnO is obtained by being repeatedly calculated a plurality of times (predetermined number of times) and averaged, before winding short-circuit determination is performed. Instead, it is also possible to store initial negative-phase-sequence current values IsnO by preparing a correspondence table of the voltage imbalance rate and the negative-phase-sequence current for each type and each rating of an electric motor.
FIG. 10 shows, in a table format, the correspondence relationship between the voltage imbalance rate and the negative-phase-sequence current. First, a method for preparing this table will be described. A row of array Vun(n) and a row of voltage imbalance rate Vunbal are prepared. In the case where the threshold δ2 predetermined for the voltage imbalance rate Vunbal is 1%, the ranges of the voltage imbalance rates Vunbal (%) corresponding to ten equally divided arrays Vun(0), Vun(1), Vun(2), ..., Vun(7), Vun(8), Vun(9) are 0 ≤ Vunbal ≤ 0.1, 0.1 < Vunbal ≤ 0.2, 0.2 < Vunbal ≤ 0.3, ..., 0.7 < Vunbal ≤ 0.8, 0.8 < Vunbal ≤ 0.9, 0.9 < Vunbal ≤ 1.0, respectively.
Regarding an electric motor of type P and rating Q, the voltage imbalance rate is calculated, and if the voltage imbalance rate is not greater than 1%, the negative-phase-sequence current is calculated. The negative-phase-sequence current value and the voltage imbalance rate are stored as a set. Then, the negative-phase-sequence current and the voltage imbalance rate are stored for a certain period, and thereafter, the average of the negative-phase-sequence current is calculated for each voltage imbalance rate, whereby the initial negative-phase-sequence current value for each voltage imbalance rate is determined. For example, the negative-phase-sequence current value Isn(1)1 when the voltage imbalance rate is 0.15% is stored in the column of negative-phase-sequence current Isn(1) in the array Vun(1). When calculation has been performed a predetermined number of times m in the array Vun(1), the m values of negative-phase-sequence current Isn(1) corresponding to Vun(1) are averaged to obtain Isn0(1). In this way, the initial negative-phase-sequence currents Isn0(n) corresponding to the ten divided arrays Vun(n) are calculated to obtain a table.
In the case of performing winding short-circuit determination for an electric motor of type P and rating Q, for example, in accordance with the flowchart in FIG. 9, the voltage imbalance rate is calculated in step S44. The initial negative-phase-sequence current value corresponding to the calculated voltage imbalance rate is read from the table stored in the storage device 11. Using the read initial negative-phase-sequence current value and the negative-phase-sequence current calculated in step S46, the evaluation value A = |Isn - Isn0| is calculated in step S47, to perform winding short-circuit determination.
In an electric motor for which the voltage imbalance rate has been acquired at the time of preparing the table of the correspondence relationship between the voltage imbalance rate and the negative-phase-sequence current shown in FIG. 10 above, a system of a control center using the electric motor, or a system in which the voltage imbalance rate is already known, it is possible to use the values in the table on the basis of the type and the rating of the electric motor and the voltage imbalance rate, without calculating the initial negative-phase-sequence current value.
As described above, according to embodiment 3, it becomes possible to perform winding short-circuit determination without calculating the initial negative-phase-sequence current value before winding short-circuit determination.
Although the disclosure is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects, and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations to one or more of the embodiments of the disclosure.
It is therefore understood that numerous modifications which have not been exemplified can be devised without departing from the scope of the present disclosure. For example, at least one of the constituent components may be modified, added, or eliminated. At least one of the constituent components mentioned in at least one of the preferred embodiments may be selected and combined with the constituent components mentioned in another preferred embodiment.

DESCRIPTION OF THE REFERENCE CHARACTERS

1 main circuit
2 circuit breaker
3 electromagnetic contactor
4 instrument transformer
5 electric motor
6 mechanical equipment
7 current detection circuit
8 instrument voltage transformer
9 voltage detection circuit
10 calculation processing unit
11 storage device
12 setting circuit
13 indication unit
14 drive circuit
15 external output unit
16 communication circuit
20 current conversion unit
20a current voltage conversion unit
21 effective value calculation unit
22 negative-phase-sequence current calculation unit
23 voltage imbalance rate calculation unit
30 initial analysis unit
31 initial negative-phase-sequence current analysis unit
40 determination unit
41 driving state determination unit
42 voltage imbalance determination unit
50 analysis unit
51 evaluation value analysis unit
60 abnormality determination unit
61 winding short-circuit determination unit
100 electric motor diagnosing device
200 monitoring device

Claims

An electric motor diagnosing device comprising:
a current detection circuit for detecting current of an electric motor; and

a calculation processing unit which receives output of the current detection circuit and performs determination for winding short-circuit abnormality in the electric motor, wherein

the calculation processing unit includes
a driving state determination unit which calculates an effective value from current of the electric motor to determine a driving state thereof,

an initial negative-phase-sequence current analysis unit for analyzing initial negative-phase-sequence current in a normal state, and

a winding short-circuit determination unit which calculates an evaluation value for winding short-circuit on the basis of a difference between negative-phase-sequence current calculated from current of the electric motor during driving and the analyzed initial negative-phase-sequence current, and performs determination for winding short-circuit of the electric motor through comparison between the evaluation value and a set threshold.
The electric motor diagnosing device according to claim 1, further comprising a voltage detection circuit for detecting voltage of the electric motor, wherein
the calculation processing unit includes
the driving state determination unit which calculates effective values from current and voltage of the electric motor to determine a driving state thereof,

a voltage imbalance rate determination unit which calculates a voltage imbalance rate from voltage of the electric motor and compares the calculated voltage imbalance rate and a set threshold to determine whether or not to perform winding short-circuit determination,

the initial negative-phase-sequence current analysis unit which analyzes initial negative-phase-sequence current in a normal state, when the voltage imbalance rate determination unit determines that winding short-circuit determination is to be performed, and

the winding short-circuit determination unit which, when the voltage imbalance rate determination unit determines that winding short-circuit determination is to be performed, calculates an evaluation value for winding short-circuit on the basis of a difference between negative-phase-sequence current calculated from current of the electric motor during driving and the analyzed initial negative-phase-sequence current, and performs determination for winding short-circuit of the electric motor through comparison between the evaluation value and a set threshold.
The electric motor diagnosing device according to claim 1, further comprising a storage device which stores a table obtained by acquiring, in advance, negative-phase-sequence current for each predetermined voltage imbalance rate range, for each type and each rating of an electric motor, and averaging a plurality of the acquired negative-phase-sequence currents, to set the averaged value as an initial negative-phase-sequence current value for each voltage imbalance rate range, wherein
the initial negative-phase-sequence current analysis unit reads, from the storage device, the table prepared for each type and each rating of the electric motor and storing the initial negative-phase-sequence current value for each predetermined voltage imbalance rate range, and uses the read initial negative-phase-sequence current value as a value of initial negative-phase-sequence current corresponding to a voltage imbalance rate of the electric motor acquired in advance.
The electric motor diagnosing device according to claim 2, further comprising a storage device which stores a table obtained by acquiring, in advance, negative-phase-sequence current for each predetermined voltage imbalance rate range, for each type and each rating of an electric motor, and averaging a plurality of the acquired negative-phase-sequence currents, to set the averaged value as an initial negative-phase-sequence current value for each voltage imbalance rate range, wherein
when the voltage imbalance rate determination unit determines that winding short-circuit determination is to be performed, the initial negative-phase-sequence current analysis unit reads, from the storage device, the table prepared for each type and each rating of the electric motor and storing the initial negative-phase-sequence current value for each predetermined voltage imbalance rate range, and uses the read initial negative-phase-sequence current value as a value of initial negative-phase-sequence current corresponding to the calculated voltage imbalance rate.